Evidence for ‘grandmother cells’

This week’s edition of the science journal Naturereports that single brain cells may be specialised for recognising specific faces.

This is an interesting finding, as it provides support for a derided hypothesis known as the ‘grandmother cell‘ theory, that was thought up to ridicule attempts to reduce human experience down to smaller and smaller components of the brain.

Neuroscience often develops by trying to understanding how smaller parts of the brain support larger processes. Bologist Jerry Lettvin argued that we can’t expect everything to reduce down to the smallest level, as some things will be distributed across the brain.

It is unlikely, he argued, that there is a single brain cell to represent each person we know, a neuron that is active when we see our grandmother, for example.

This has since been used as an argument against any theory that is seen as over-simplifying how things are represented in the brain.

But now, a team led by neuroscientist Rodrigo Quian Quiroga has identified neurons which do seem to be active for individual faces.

He implanted harmless electrodes into the temporal lobes of volunteers undergoing surgery for epilepsy.

Quiroga then showed the participants pictures of famous faces, and discovered some cells were only active for individual faces in the set – Halle Berry, or even members of The Simpsons.

Of course, it’s impossible to say whether these cells are truly selective for an individual face out of all the ones a person may know, but this level of selectivity is a great surprise for those who thought individual cells would be active for very general features of the visual world.

One Comment

There’s a theoretical reason why the ‘grandmother cell’ argument still holds, of course. At the limit local representations (ie each thing represented by a specific cell, and each specific cell representing a single thing) means there is no generalisation: you need a cell for your grandmother as you saw here first today, and a cell for seeing your grandmother holding a warm cake, and a cell for seeing your grandmother smiling, etc etc. We’re only able to comprehend the idea of a grandmother because we can absorb many different (and quite diverse) physical sensations into the single concept, and (maybe!) represent that single concept in a single cell or set of cells.